1. Field of the Invention
Embodiments disclosed here generally relate to cutter pockets for use on downhole tools. More specifically, embodiments disclosed herein relate to cutter pockets for top loading cutters. More specifically still, embodiments disclosed herein relate to substantially square cutter pockets for top loading cutters.
2. Background Art
FIG. 1 shows one example of a conventional drilling system for drilling an earth formation. The drilling system includes a drilling rig 10 used to turn a drilling tool assembly 12 that extends downward into a well bore 14. The drilling tool assembly 12 includes a drilling string 16, and a bottomhole assembly (BHA) 18, which is attached to the distal end of the drill string 16. The “distal end” of the drill string is the end furthest from the drilling rig.
The drill string 16 includes several joints of drill pipe 16a connected end to end through tool joints 16b. The drill string 16 is used to transmit drilling fluid (through its hollow core) and to transmit rotational power from the drill rig 10 to the BHA 18. In some cases the drill string 16 further includes additional components such as subs, pup joints, etc.
The BHA 18 includes at least a drill bit 20, also known as a primary cutting structure. Typical BHA's may also include additional components attached between the drill string 16 and the drill bit 20. Examples of additional BHA components include drill collars, stabilizers, measurement-while-drilling (MWD) tools, logging-while-drilling (LWD) tools, subs, hole enlargement devices also known as secondary cutting structures (e.g., hole openers and reamers), jars, accelerators, thrusters, downhole motors, and rotary steerable systems.
Referring to FIGS. 2 and 3 together, cutting tools including, for example, drill bits, hole openers, and reamers, work by engaging and removing formation. Typically, the body 30 of the cutting tool includes a plurality of cutting elements 32, 34 each having a cutting face 42, 44 that engages the formation.
Cutting elements 32, 34 are conventionally attached to cutter pockets 36 disposed in the cutting tool body 30. The cutter pockets 36 typically feature at least one scooped portion 38 to allow cutting elements 32, 34 to be loaded into the cutter pocket from the front or the back. The scoop 38 of the cutter pocket 36 increases the minimum distance 40 between the cutting faces 42, 44 of the cutting elements. As a result, the number of cutters that may be placed on a cutting tool body 30 of limited size is decreased.
Cutting elements 32, 34 may be disposed on drilling tools according to several processes. Specifically, cutting elements 32, 34 may be disposed as either top loading cutters (meaning the cutting elements are disposed in cutter pockets from the top of a tool) or front loading cutters (meaning the cutting elements are disposed in cutter pockets from the front of a tool). Top loading cutting elements may be used in various downhole tools. Examples of such tools may include fixed cutter drill bits, also known in the art as drag bits or PDC bits, milling devices, and mill-head thereof, hole opening devices, such as reamers, and other various tools knows to those of ordinary skill in the art. Similarly, front loading cutting elements may also be used in various downhole tools, such as drill bits, milling devices, and hole opening devices.
Methods used to create cutter pockets and to affix cutting elements therein include numerous steps. Typically, the cutter pocket 36 is machined into the cutting tool body 30 using electric discharge machining (EDM) or laser machining. Next, the cutting tool body 30 is pre-heated in preparation for welding. The welding process is performed to create at least one shoulder 46 in the cutter pocket 36 on which the cutting element 32 abuts. After the welding is complete, the cutting tool body and the welded shoulders 46 are allowed to cool, which may require up to 30 hours. During the cooling process, stresses may be introduced at the interface 48 of the cutting tool body 30 and the weld metal 50 due to the difference in material properties. In some instances, the stresses may initiate cracks at the interface 48 of the cutting tool body 30 and the weld metal 50.
After the weld 50 and the cutting tool body 30 cool to a desired temperature, the weld metal 50 is cleaned of welding residue using a grinding process performed manually. This process may also be used to shape the weld shoulder 46 and to remove any irregular surfaces. The imprecise nature of the manual shaping process may prevent manufacturers from achieving the tolerances indicated in the original cutter pocket design.
Next, cutting elements 32, 34 are inserted into cutter pockets 36 so as to abut the weld shoulders 46. The cutting elements 32, 34 are typically fixed to the cutter pockets 36 using a brazing process. The bond created by the braze disposed between the weld metal 50 and the cutting elements 32, 34, typically weaker than the bond created by braze between the tool body 30 and the cutting element 32, 34. Additionally, during brazing, localized heating occurs which, consequently, requires cooling to take place. The cooling occurs at the interface between the braze metal 52 and the weld metal 50, and occurs at the interface between the braze metal 52 and the tool body 30. Due to differences in material properties, variable alignment, and dealignment of different material grains, cracks may initiate at the interfaces between the braze metal 52, the weld metal 50, and tool body 30.
Accordingly, there exists a need for a cutter pocket geometry that allows for a decreased distance between cutting elements, as well as methods of manufacturing downhole tools including such cutter pocket geometry.